Method of drying fibrous material



H. C-v'. WALKER E" AL METHOD 0F' DRYING FIBROUS MATERIAL May 1, 1934.

Filed Sept. 25, 1929 Patented May l, 1934 UNITED STATES ,PATENT OFFICE METHOD OF DRYING FIBROUS MATERIAL Howard G. Walker, La Grange, and Albert T. March, Western Springs, lll., assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application September 25, 1929, Serial No. 394,950

3 Claims.

This invention relates to a method of and apparatus for drying brous material, more particularly paper or pulp insulation on electrical conductors for use in telephone cables.

In the grouping of a large number of individual conductors in a single sheath or cable for use in telephonie communicating systems, it is essential that the conductors be insulated from each other and have a minimum electrostatic capacity.

Since dry air possesses a very high electrical resistance and a very low inductive capacity, the retention of as much dry air as possible around each conductor becomes of great importance in the manufacture of insulated conductors for electric cables.

The primary object of the invention is to provide a simple method of and apparatus for rapidly drying fibrous materials to improve the physical and dielectric properties thereof.

In accordance with one embodiment, the invention contemplates the provision of an apparatus by means of which the method may be practiced in drying pulp insulation on an electrical conductor, wherein the insulated conductor is 5 drawn from the pulp applying mechanism at a predetermined rate through an electrical radiant heat dryer having a plurality of contiguous heat zones varying from a temperature of approximately 800o C. at the point of entrance to a temperature of approximately 400 C. at the exit.

Other objects and advantages of the invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawing, wherein Fig. 1 is a side elevational view of an electrical radiant heat drying apparatus associated with a pulp applying mechanism whereby the improved method of drying may be practiced;

Fig. 2 is an enlarged transverse sectional view of the drying apparatus taken on line 2 2 of Fig. 1;

Fig. 3 is a fragmentary side elevational view, partly in section, of another type of radiant heater for drying simultaneously pulp insulation on a plurality of conductors, and

Fig. 4 is a transverse sectional view thereof taken on line 4-4 of Fig. 3.

Referring now to the drawing in which like reference numerals designate similar parts throughout the various views, the core or conductor 10 is drawn from a supply reel 11 over a pulley 12 and thence around a drum 13 which is partially submerged in a liquid containing pulp within a semi-circular tank 14. The periphery of the drum 13 is provided with a plurality of relvductor and coating' are passed through the atively large perforations (not shown) which are covered with fine wire mesh. The drum has a centrally disposed tubular axle which is suitably mounted within bearings 15 carried by a framework 20.

In order to apply pulp to a conductor as it passes over the drum, the liquid within the drum is maintained at a lower level than that of the pulp mixture inthe tank 14, as indicated by dotted lines 21 and 22, respectively. This difference in 65 levels is maintained by a siphon pipe 23 which has its inlet openings submerged in the liquid within the drum 13 and is discharged through a tubular axle 24. A continuous circulation of the pulp mixture is maintained in the tank by feeding the pulp mixture from a supply tank 25 into the tank 14 and out of there to a pipe 26 into a` receiving tank (not shown) from which it is pumped back into the supply tank 25 inany suitable manner. As the drum carries the conductor supported on the wire mesh through the tank, due to the difference in the levels of the liquid within the drum 13 and the tank 14, the liquid in the tank will pass through the wire mesh, straining the pulp onto the outer surface of the mesh and applying pulp to the conductor supported thereon.

As the drum is rotated in the direction indicated by the arrow in Fig. 1, the conductor with its pulp coating thereon leaves the drum at the top and the force of gravity, the surface tension of the liquid in the pulp mixture, and the felting action of the pulp fibers cause it to surround and cling to the conductor. From the drum the pulp .covered conductor is passed over an auxiliary roll 30 and then between a pairof squeezing rolls 3l and 32. Suitable means (not shown) is provided for driving the roll 32, and this roll and the roll 31 preferably draw the conductor from the supply reel l1 over the drum, causing it to r0- tate. The auxiliary roll 30 is made foraminous where it engages the pulp coating of the conduc- -tor in order that the excess liquid may be strained therefrom Without causing a back flow of the liquid, which would tend to wash oii. the pulp coating which at this stage of the process is very soft and moist and easily removed from the conductor. This removal of the excess liquid imparts greater strength to the pulp coating due to a closer felting of the bers so that when the consqueezing rolls the coating will not be torn from the conductor.

From the squeezing rolls the conductor with its pulp 'coating is drawn through a rapidly rotating former 35 which wipes the projecting edges of 110 jpulp applying mechanism reference may be had :to H. G. Walker and A. T. March Patent No.

i eo

From the former 35 the pulp covered conductor is drawn through an electrical radiant heat dryer 39 by a take-up reel 40 mounted on the framework 20 and driven' by any suitable means (not shown). The electrical radiant heat-dryer comprises a chamber or tube'42 (Fig. 2) and a wrapping of asbestos sheet 43 over which is wound a resistor 44, the turns thereof being close together at the entrance end nearest the former 35 and the spacing between the turns gradually increas-v ing as the resistor approaches the exit end of the tube. The resistor is connected in series with an electric generator 45 and a rheostat 46 whereby the electric current may be controlled to obtain a temperature of approximately 800 C. at the entrance of the tube, the temperature gradually decreasing to 400" C. at. the exit end thereof. In order to prevent loss of heat due to radiation outwardly from the tube, the tube and the resistorare covered by a thick coatof asbestos 47 whichfis held in place by a casing 48 suitably mounted on the framework 20.

The pulp covered conductor is drawn through the hot tube, which is about 20 feet in length, at the rate of approximatelylOO feet per minute so as to prevent scorching or burning of the pulp insulation. The speed at which a pulp covered conductor should travel through the radiant heat is determined by the length of the tube, the thickness of the pulp coating, and thertemperature. It has been found that paper or pulp rapidly dried at high temperatures and ordinary atmospheric pressures is thicker and of lower density, having greater porosity, the shrinkage is greatly reduced, and the strength thereof increased.

In Figs. 3 and 4 is shown an improved type o! electrical radiant heat dryer 55 for drying slmulg taneously a plurality of pulp covered conductors. This dryer comprises a tunnel or box type furnace forming a chamber having a hearth 56 of refractory material which is partially enclosed by a high temperature insulation 57 and a low temperature insulation 58. The top of the furnace is divided into three removable roof sections 59, 60, and 6l, each section including a plurality of fire bricks 62-62 (Fig. 4) forming an arch, in grooves 63 of which are mounted T supports 64--64 for holding electrical heating resistors 65 in position.'

Over the arch are placed high temperature insulation 66 and low temperature insulation 67. The furnace is encased in a reinforced steel shell 69 which is suitably secured to a plurality of steel beams 70--70. As diagrammatically shown in Fig. 3, the resistors 65 of each section are connected to an electric generator and independently controlled by rheostats 76, 77, and 78, so that three contiguous heating zones having temperatures of approximately 800 C., 600 C., and 400 C. can be maintained, the highest temperature being at the entrance end of the dryer and the lowest at the exit thereof. The electrical resistors heat the refractory arch to incandescence and the heat therefrom is reflected from the hearth to thoroughly and quickly dry the pulp insulation.

Although the invention herein described and illustrated is particularly well adapted to dry pulp insulation on electrical conductors used in telephone cables, it will be understood that the invention is capable of many other modifications and applications and is to be limited only by the scope of the appended claims.

What is claimed is:

l. The method of insulating a core with pulpous material, which consists in applying a pulpous material on the core, and subjecting the core and pulpous material to a high initial scorching temperature and gradually reducing the temperature to prevent scorching, thereby drying and increasing the porosity of the pulpous material.

2. The method of rapidly insulating an electrical conductor with pulpous material, which consists in applying moist pulp on the conductor, shaping the pulp on the conductor to a predetermined contour, and moving the coated conductor through a substantially closed chamber, the atmosphere at the entrance thereof having an initial temperature of approximately 800 C. and a negative temperature gradient to dry the material and increase the porosity of the pulpous material.

3. The method of rapidly insulating an electrical conductor with pulpous material, which consists in coating the conductor with moist loosely felted pulpous material, and subjecting the pulpous coating to an atmosphere having a negative temperature gradient and temperature ranging fromapproximately 800 C. to 400 C. for approximately 20 seconds to dry the pulpous coating with a. minimum of shrinkage and to increase the porosity of the material.

HOWARD G. WALKER. ALBERT T. MARCH. 

